1. Field of the Invention
The present invention relates to a high pressure fuel supply apparatus chiefly for use in a cylinder fuel injection engine or the like.
2. Description of the Related Art
FIG. 10 is a configuration diagram showing a fuel supply system in an internal combustion engine for a vehicle, including a related-art high pressure fuel supply apparatus. In FIG. 10, fuel 2 in a fuel tank 1 is delivered from the fuel tank 1 by a low pressure pump 3, passed through a filter 4, adjusted in pressure by a low pressure regulator 5, and then supplied to a high pressure fuel supply apparatus 6 which is a high pressure pump. Only a flow rate of the fuel 2 required for fuel injection is boosted by the high pressure fuel supply apparatus 6, and supplied into a delivery pipe 9 of a not-shown internal combustion engine. A surplus of the fuel 2 is relieved between a low pressure damper 12 and a suction valve 13 by an electromagnetic valve 17.
In addition, the required fuel flow rate is determined by a not-shown control unit, which also controls the electromagnetic valve 17. The high pressure fuel supplied thus is injected into a cylinder of the internal combustion engine in the form of high pressure mist from a fuel injection valve 10 connected to the delivery pipe 9. When abnormal pressure (high relief valve opening pressure) is placed in the delivery pipe 9, a filter 7 and a high pressure relief valve 8 are opened to prevent the delivery pipe 9 from being broken.
The high pressure fuel supply apparatus 6 which is a high pressure pump, has a filter 11 for filtering the supplied fuel, a low pressure damper 12 for absorbing the pulsation of the low pressure fuel, and a high pressure fuel pump 16 for pressurizing the fuel supplied through the suction valve 13 and discharging the high pressure fuel through a discharge valve 14.
FIG. 11 is a sectional view showing a related-art high pressure fuel supply apparatus. In FIG. 11, the high pressure fuel supply apparatus 6 has a casing 61, a high pressure fuel pump 16, an electromagnetic valve 17, and a low pressure damper 12, integrally. The high pressure fuel pump 16 is a plunger pump provided in the casing 61.
A fuel pressurizing chamber 163 surrounded by a sleeve 160 and a plunger 161 inserted slidably in the sleeve 160 is formed in the high pressure fuel pump 16. The other end of the plunger 161 abuts against a tappet 164, and the tappet 164 abuts against a cam 100 so as to drive the high pressure fuel pump 16. The cam 100 is provided integrally or coaxially with a cam shaft 101 of the engine so as to reciprocate the plunger 161 along the profile of the cam 100 in cooperation with the rotation of a crank shaft of the engine. The volume of the fuel pressurizing chamber 163 is changed by the reciprocating motion of the plunger 161 so that the fuel boosted to high pressure is discharged from the discharge valve 14.
In the high pressure fuel pump 16, a plate 162, the suction valve 13 and the sleeve 160 are held between the casing 61 and an end surface of a spring guide 165, and fastened with a bolt 180. The plate 162 forms a fuel suction port 162a for sucking fuel from the low pressure damper 12 to the fuel pressurizing chamber 163, and a fuel-discharge port 162b for discharging the fuel from the fuel pressurizing chamber 163.
The suction valve 13 shaped into a thin plate is formed in the fuel suction port 162a. The discharge valve 14 is provided on the fuel discharge port 162b so as to communicate with the delivery pipe 9 through a high pressure fuel discharge passageway 62 provided in the casing 61. In addition, in order to suck fuel, a spring 167 for pushing the plunger 161 down in a direction to expand the fuel pressurizing chamber 163 is disposed in the state where the spring 167 has been compressed between the spring guide 165 and a spring holder 168. An oil seal 169 is provided to isolate the fuel in the fuel pressurizing chamber 163 from the lubricating oil of the engine.
The electromagnetic valve 17 has an electromagnetic valve body 170, a valve seat 173, a valve 174, and a compression spring 175. The electromagnetic valve body 170 is incorporated in the casing 61 of the high pressure fuel supply apparatus 6 so as to have a fuel channel 172 inside the electromagnetic valve body 170. The valve seat 173 is provided in the fuel channel 172 of the electromagnetic valve body 170. The valve 174 is held on/off the valve seat 173 in the electromagnetic valve body 170 so as to close/open the fuel channel 172. The compression spring 175 presses the valve 174 onto the valve seat 173.
At a point of time when a flow rate requested from a not-shown control unit has been discharged in a discharge stroke of the high pressure fuel pump 16, a solenoid coil 171 of the electromagnetic valve 17 is excited to open the valve 174. Thus, the fuel 2 in the fuel pressurizing chamber 163 is released to the low pressure side between the low pressure damper 12 and the suction valve 13 so that the pressure in the fuel pressurizing chamber 163 is reduced to be not higher than the pressure in the delivery pipe 9. Thus, the discharge valve 14 is closed. After that, the valve 174 of the electromagnetic valve 17 is opened till the high pressure fuel pump 16 proceeds to a suction stroke. The timing to open the electromagnetic valve 17 is controlled so that the amount of fuel discharged into the delivery pipe 9 can be adjusted.
However, the related-art high pressure fuel supply apparatus has problems as follows. FIG. 12 is an enlarged sectional view showing the vicinity of the oil seal in the high pressure fuel pump of the related-art high pressure fuel supply apparatus. As shown in FIG. 12, the oil seal 169 is constituted by an annular portion 169a, a seal portion 169b made of rubber, and a spring 169c. The annular portion 169a is fixed to the inner wall surface of the bolt 180 by press fitting. The seal portion 169b is fitted to one end of the annular portion 169a so as to slide on the outer circumferential wall of the plunger 161. The spring 169c is attached to the seal portion 169b so as to always press the outer circumferential wall of the plunger 161 at predetermined pressure. In addition, the other end of the annular portion 169a opposite to the seal portion 169b is formed as an open end 169d. 
As for the method for manufacturing the oil seal 169, first, an adhesive agent is applied to the surface of the annular portion 169a. After that, the rubber seal portion 169b is bonded and fixed, by vulcanizing molding, to the edge of an insertion hole for the plunger 161 formed at one end of the annular portion 169a. At this time, the adhesive agent applied to the surface of the annular portion 169a also adheres to a portion abutting against the inner wall surface of the bolt 180. When the adhesive agent is dried, the adhesion state of the adhesive agent varies markedly. When press fitting is carried out in this state, there is a problem that a failure in sealing occurs in the abutment portion.
FIG. 13 is a graph showing the relationship between the press-in load and the press-in stroke of the oil seal 169. In FIG. 13, the ordinate designates the press-in load (kN), and the abscissa designates the press-in stroke. In addition, FIG. 14 is a graph showing the surface pressure distribution generated in the abutment portion between the oil seal 169 and the bolt 180. In FIG. 14, the ordinate designates the axial position of the abutment portion between the oil seal 169 and the bolt 180, and the abscissa designates the surface pressure (MPa).
As shown in FIG. 13, at the beginning of press fitting of the annular portion 169a, that is, at the beginning of a press-in stroke, a high press-in load is generated. After that, however, the press-in load is lowered with the advance of the press fitting, and then reaches a substantially constant value. This is because the annular portion 169a is formed out of a thin metal plate about 1 mm thick. That is, while the press-in load is generated at the beginning of the press fitting, the open end 169d side of the annular portion 169a, that is, the vicinity of a point B in FIG. 11 is deformed in the inner diameter in the second half of the press-in stroke, so that the press-in load is lowered. Thus, as shown in FIG. 14, the portion where high surface pressure is generated, that is, the seal position is formed near a point A. As a result, surface pressure required for sealing cannot be secured in the vicinity of the point B, so that seal function is hardly provided.
In addition, the adhesive agent adhering to the vicinity of the point B of the annular portion 169a is peeled off by sliding on the inner wall surface of the bolt 180 at the time of press fitting. However, the adhesive agent adhering to the vicinity of the point A of the annular portion 169a cannot obtain a high press-in load at the time of press fitting, and there is no press-in stroke. Thus, the adhesive agent not peeled off adheres to the surface of the annular portion 169a as it is. As a result, a gap produced due to variation in the adhesion state of the adhesive agent causes a failure in sealing.
As described above, there is a problem that a failure in sealing occurs in both the vicinity of the point A and the vicinity of the point B in the annular portion 169a so that the fuel and the lubricating oil of the engine cannot be sealed perfectly.
To solve such a problem, it can be considered to take measures to mold rubber not only in the seal portion 169b but also to reach the outer circumferential wall of the annular portion 169a. In this case, there arises a new problem that the annular portion 169a becomes sizable due to the rubber, the rubber is picked at the time of press fitting, or the rubber swells in liquid so as to interfere with other parts.
The invention is developed to solve the foregoing problems. It is an object of the invention to provide a high pressure fuel supply apparatus in which sealing properties between fuel and lubricating oil of an engine are improved.
According to the invention, there is provided a high pressure fuel supply apparatus having: a plunger reciprocating and sliding in a sleeve of a high pressure fuel pump so as to form a fuel pressurizing chamber between the plunger and the sleeve to thereby discharge pressurized fuel; a specified member forming a part of a housing of the high pressure fuel pump; and a seal member fixed to an inner wall surface of the specified member by press fitting so as to slide on an outer circumferential wall of the plunger in accordance with reciprocating motion of the plunger to thereby seal the fuel and lubricating oil; wherein the specified member is formed so that a press-in load in a second half of a press-in stroke of the seal member is higher than that in a first half thereof in an abutment portion of the specified member against the seal member.
Preferably, the specified member is formed into a tapered shape whose bore diameter varies continuously in the abutment portion of the specified member against the seal member.
Preferably, the specified member is formed to have an inner wall surface constituted of a plurality of different bore diameters in the abutment portion of the specified member against the seal member.
Preferably, the specified member has a smallest bore diameter in the second half of the press-in stroke of the seal member in the abutment portion of the specified member against the seal member.